The objective of this research is to elucidate the sequence of events which occur when a cell or cells of one type is accepted or rejected by a cell, aggregate or tissue fragment of a different cell type. In particular, we are studying the difference in recognition processes between normal and cancer cells which can account for the differential inhibitory effect of normal and cancer cells on the aggregation of embryonic cells. We are investigating how these differentiated inhibitory effects may be mediated, especially with regard to modifiers of cell adhesion, metabolism, motility, and the cell periphery including cell surface enzymes. In addition to the aggregating system, we will use stationary culture, adhesion to artificial and cellular substrates, and collecting aggregates as "sensor systems" for the interaction of the normal and cancer cells.